DE 27 36 982 A1 already describes a wear resistant coating for shaped parts, especially for tools, comprised of a shaped body, preferably of hard metal, and one or more surface coatings, at least one of which is a protective layer with a ceramic matrix into which a further material is incorporated. The ceramic matrix and the material incorporated therein have different coefficients of thermal expansion so that the protective layer is subject to the formation of fine microcracks therein. Unstabilized and/or partially stabilized ZrO2 has been proposed as the material incorporated into the interstices of a ceramic matrix of Al2O3. To produce such a layer by the CVD process, AlCl3, CO2 and H2 are admitted as a gas phase into a reaction vessel at 1100° C. to produce Al2O3 or ZrCl4 and water vapor (H2O) are admitted to produce ZrO2. Because of the density difference between the tetragonal modification of ZrO2 formed at temperatures above the transformation temperature of about 1100° C. and the monoclinic modification formed below about 1100° C., with a corresponding phase conversion there can be a significant change in volume of the deposited ZrO2. As a consequence, with increasing volume proportions of the ZrO2 there is a simultaneous increase in the microcrack density in the deposited ceramic layer.
In DE 28 25 009 C2 (U.S. U.S. Pat. No. 4,180,400), a hard metal body with a thin wear-resistant surface layer of Al2O3 has been described and which is composed completely or at least 85% of the κ-modification and any possible remainder of the α-modification, forming surface regions or patches at most 10 μm in size. The aluminum oxide layer can contain further additions of titanium, zirconium and/or hafnium. To create this ceramic layer by the CVD process, the gas mixture apart from AlC3, CO2, CO and H2 has also small amounts of 0.03 to 0.5% TiCl4 added to it. This addition, however, serves exclusively or nearly exclusively for the formation of the κ-Al2O3 phase.
A further CVD process for depositing Al2O3 and/or ZrO2 using additional reagents, like hydrogen sulfide, has been described in EP 0 523 021 B1 (U.S. Pat. No. 5,674,564).
DE 195 18 927 A1 (U.S. Pat. No. 5,827,570) describes a coated cutting tool comprised of a substrate of sintered carbide or ceramic with a wear-resistant composite ceramic coating which has two different metal oxide phases, for example of Al2O3 and ZrO2 and in addition thereto a doping agent selected from the group of sulfur, selenium, tellurium, phosphorus, arsenic, antimony, bismuth or compounds of these elements. To produce this two-phase layer by a CVD process, for example AlCl3 and ZrCl4, CO2 with H2 as a carrier gas, in addition to an H2S gas, is passed over the substrate body at a temperature of about 700° to 1250° C. and a pressure from 133 Pa to ambient pressure, whereby the two-phase layer with the doping agent is deposited.
EP 0 786 536 A1 (U.S. Pat. No. 5,985,427) describes a coated hard metal body with a 3 to 30 μm thick aluminum oxide coating which has been deposited by means of CVD and/or PVD and contains 0.005 to 0.5 weight % chlorine. Optionally 0.5 to 10 weight % Zr and/or Hf and 1.5 to 15 weight % Ti can be contained in this coating.
EP 0 162 656 A2 (U.S. Pat. No. 4,746,563) describes a multilayer coating on a hard metal substrate body which is comprised of an inner layer, which is composed of at least one carbide, nitride, carbonitride, carbo-oxygen nitride, oxynitride, boron nitride or boron-carbonitride of titanium, and an outer multilayer coating with a total thickness of 5 to 20 μm and provided with an outer layer of a plurality of Al2O3 coatings with a respective thickness of 0.01 to 2 μm and each comprised of an Al2O3 film in which titanium oxide has been dissolved or which has been codeposited with at least 30 volume percent titanium oxide. The layers are separated by intervening layers with respective thicknesses of 0.01 to 2 μm and which each can comprise TiC, TiN, TiCN, TiCNO, TiNO, titanium oxides, Ti(B,N), Ti(B,N,C), SiC, AlN or AlON.
In WO 00/17 416 (U.S. Pat. No. 6,660,371), a composite material of a coated hard metal or cermet base body has been described on which the single layer or a multilayer coating is applied at least in the form of a 0.5 μm to 25 μm thick coating and preferably the outermost phase is an Al2O3 phase containing a ZrO2 and/or HfO2 phase which in turn contains a third fine dispersive phase consisting of an oxide, oxycarbide, oxynitride or oxycarbonitride of titanium. The proportion of the third phase in the overall composition of this layer amounts to 0.2 to 5 mol %. To produce such a three phase layer, a CVD process with deposition temperatures between 900° C. and 1000° C. is selected in which the gases required for the deposit contain chlorides of the Al, Zr and Hf, and in addition CO2, H2, CH4 and N2 or inert gas under pressures of 10 to 100,000 Pa. The TiOx incorporated as the third phase has a positive effect on the growth speed and on the particle sizes of the aluminum oxide and zirconium or hafnium oxide. Preferably a coating temperature of 960° C. is selected in which the ZrO2 is present in the monoclinic form. From the mentioned publication, therefore, hard metal substrate bodies are known which have layer sequences TiN—Ti(C,N) and the described three phase layer.